THORIUM.

The atomic weight of thorium has been determined from analyses of the sulphate, oxalate, formate, and acetate, with widely varying results. The earliest figures are due to Berzelius,* who worked with the sulphate, and with the double sulphate of potassium and thorium. The thoria was precipitated by ammonia, and the sulphuric acid was estimated as BaSO. The sulphate gave the following ratios in two experiments. The third column represents the weight of ThO, proportional to 100 parts of BaSO4:

.6754 grm. Tho, = 1.159 grm. BaSO.. 1.0515

66

1.832

66

Ratio, 58.274

57.396

The double potassium sulphate gave .265 grm. ThO,, .156 grm. SO,, and .3435 K2SO. The SO,, with the Berzelian atomic weights, represents .4537 grm. BaSO.. Hence 100 BaSO, is equivalent to 58.408 ThO,. This figure, combined with the two previous values for the same ratio, give a mean of 58.026, .214. Hence Tho2 =269.940, .997.

2

From the ratio between the K,SO, and the Tho, in the double sulphate, ThO, 268.284.

=

In 1861 new determinations were published by Chydenius,† whose memoir is accessible to me only in an abstract ‡ which gives results without details. Thoria is regarded as a monoxide, ThO, and the old equivalents (08) are used. The following values are assigned for the molecular weight of ThO, as found from analyses of several salts:

From Sulphate. From K. Th. Sulphate.

* Poggend. Annal., 16, 398. 1829. Lehrbuch, 3, 1224.

+ Kemisk undersökning af Thorjord och Thorsalter. Helsingfors, 1861. An academic dissertation.

† Poggend. Annal., 119, 55. 1863.

We may fairly assume that these figures were calculated with O = 8, C6, and S = 16. Correcting by the values for these elements which have been found in previous chapters, ThO, becomes as follows:

The single result from the double potassium sulphate is included with the column from the ordinary sulphate, and the influence of the atomic weight of potassium is ignored.

Chydenius was soon followed by Marc Delafontaine, whose researches appeared in 1863.* This chemist especially studied thorium sulphate; partly in its most hydrous form, partly as thrown down by boiling. In Th(SO4)2.9H,O, the following percentages of ThO, were found:

45.08

44.90

45.06

45.21

45.06

Mean, 45.062, ± .0332

Hence ThO, =263.637, .256.

The lower hydrate, 2Th(SO4)2.9H2O, was more thoroughly investigated. The thoria was estimated in two ways; first, (A,) by precipitation as oxalate and subsequent ignition; second, (B,) by direct calcination. These percentages of ThO, were found:

2

* Arch. des Sci. Phys. et Nat., (2,) 18, 343.

In three experiments with this lower hydrate the sulphuric acid was also estimated, being thrown down as barium sulphate after removal of the thoria:

The figures in parenthesis are reproduced by myself from Delafontaine's results, he having calculated his analyses with O = 100, S=200, and Ba= 857. These data may be reduced to a common standard, so as to represent the quantity of 2Th(SO4)2.9H2O equivalent to 100 parts of BaSO4. then have the following results:

We

Delafontaine seems himself to have calculated from the ratio between the percentages of SO, and ThO2; whence, with our revised values for S, Ba, and O, ThO, 262.643. Delafontaine's work was soon confirmed by Hermann,*

* Journ. für Prakt. Chem., 93, 114.

=

who published a single analysis of the lower hydrated sulphate, as follows:

Hence, from the ratio between SO, and ThO,, ThO, = 263.030. Probably the SO, percentage was loss upon calcination.

The latest, and probably also the best determinations, are those of Cleve,* whose results, obtained from both the sulphate and the oxalate of thorium, agree admirably. The anhydrous sulphate, calcined, gave the subjoined percentages of thoria:

62.442

The oxalate was subjected to a combustion analysis, whereby both thoria and carbonic acid could be estimated. From the direct percentages of these constituents no accurate value can be deduced, there having undoubtedly been moisture in the material studied. From the ratio between CO, and ThO2, however, good results are attainable. This ratio I put in a fourth column, making the thoria proportional to 100 parts of carbon dioxide:

Mean, 151.114, ± .053

Hence ThO, =265.357,.104.

*K. Svenska Vet. Akad. Handlinger. Bd. 2, No. 6. 1874.

There are now before us twelve estimates for the molecular weight of thoria. Two of these represent single experiments, and have no probable error attached to them; namely, the one due to Hermann, and the one deduced from Berzelius' K,SO, ThO, ratio. A third value, from Delafontaine's sulphuric acid estimations, has so high a probable error that it could be rejected without influencing the general mean. These three values might all be excluded without serious objection; but it is perhaps better to arbitrarily assign them equal weight, average them together, and give their mean the same probable error as that which attaches to Berzelius' BaSO, ThO, series. This mean is indicated as "A" in the following combination :

262.804, .493

66

=

263.637,±.256

66

=

266.025,

.363

=

265.380,

.123

66

=

265.357,.104

66

= 265.341, .072

General mean_

Hence Th= 233.414, .0725; or, if O = 16, Th = 233.951.

These values vary from those derived from Cleve's experiments alone only in the second decimal.

GALLIUM.

Gallium has been so recently discovered, and obtained in such small quantities, that its atomic weight has not as yet been determined with much precision. The following data were fixed by the discoverer, Lecoq de Boisbaudran: *

*Journ. Chem. Soc., 1878, p. 646.